AC adaptor with power consumption reduction in unused state

ABSTRACT

An AC adaptor that can reduce power not in use state, and a battery-operated electronic apparatus that can employ such an AC adaptor. An AC adaptor includes, (a) an input line along which an external AC voltage is input, (b) a first transformer for transforming the input AC voltage into a DC voltage at a first voltage level, (c) a switch provided on the primary side of the first transformer, (d) an output line along which a DC voltage on the secondary side of the first transformer is output externally, (e) a second transformer for transforming the input AC voltage into a DC voltage at a second voltage level that is higher than the first voltage level and for outputting the resultant DC voltage to the output line, and (f) an AC adaptor operation control circuit for comparing a voltage level across the output line with a reference voltage level, which is higher than the first voltage level and which is lower than the second voltage level, and for turning on the switch when the voltage level across the output line is lower than the reference voltage level, or for turning off the switch when the voltage level across the output line exceeds the reference voltage level. When an electronic apparatus does not require supply of power, the AC adaptor is detached from the system load in the apparatus, so that the voltage across the output line of the AC adaptor exceeds the reference voltage. In response to the result of the comparison, the switch on the primary side of the first transformer is turned off, and thus the operation of the first transformer can be halted.

RELATED PATENT FILING

This patent document is cross referenced to assignee's related patentdocument Ser. No. 09/195,815.

FIELD OF THE INVENTION

The present invention relates to an AC adaptor for transforming acommercially available AC voltage into a DC voltage and to abattery-operated electronic apparatus that can employ such an ACadaptor, and in particular to an AC adaptor for which power can bereduced in the unused state and to a battery-operated electronicapparatus that can employ such an AC adaptor. More specifically, thepresent invention pertains to an AC adaptor for which power consumptioncan be reduced in the unused state by detecting the state of a powersource in an electronic apparatus connected thereto, and to abattery-operated electronic apparatus that can employ such an ACadaptor.

BACKGROUND OF THE INVENTION

In accordance with recent technical developments, various types ofpersonal computers, such as desktops, towers and notebooks, are beingproduced and sold. Notebook computers, designed for outdoor use whiletaking into consideration the mobility and portability, are compact andlight. A typical example of such a notebook computer is the “IBMThinkPad 770” series sold by IBM Japan, Co., Ltd (“IBM ThinkPad 770” isa trademark of IBM Corporation).

Almost all the notebook PCS can be operated by incorporated batteriesbecause this type of PC can even be employed in a mobile environmentwhere AC power is not available. An incorporated battery is provided asa “battery pack” in which are stored a plurality of rechargeable batterycells, such as Li-Ion, NiCd or NiMH battery cells.

While the capacity of an AC power source is generally considered to beunlimited, the capacity of the battery pack is always limited and itsoperating period is short (usually, at most, two to three hours), and anextended period of time is required to recharge it (generally, the timerequired for charging is the equivalent of the operating period for thebattery). A user can carry a spare battery to extend the effectivebattery operating period; however, since a spare battery isinconvenient, heavy and bulky, portability is degraded. Therefore, in anoffice environment where AC power is available, an external AC adaptoris connected to a notebook computer to drive it using the AC power. TheAC adaptor is a device for transforming an AC voltage into a DC voltage,and includes a rectifier and a transformer for transforming the level ofa DC voltage, which is well known. A cable extending from one end of anAC adaptor is inserted into an AC outlet (normally built into a wall ina room), and another cable extending from the other end of the ACadaptor is inserted into a DC inlet in the case of a notebook PC. Poweroutput by the AC adaptor is used to drive the apparatus, as is describedabove, and extra power or power supplied in the power-off state is usedto recharge an incorporated battery.

Recent notebook PCS are capable of replacing desktops, i.e., can serveas “desktop replacements.” This is because, as the semiconductorfabrication techniques have been developed, the processing capabilitiesof notebook computers have been improved until they are equivalent tothose of desktop PCS, and also because the size of an LCD panel screenand the number of drive units have been increased and the workingenvironment for notebook PCS is as excellent as is that for the desktopPCS. In addition, since a notebook PC has a smaller volume and a smallfootprint, installation space in an office environment can be saved.

When a notebook PC is used only in an office, an AC power source isemployed, as is described above. In most cases, a notebook PC that isused in this manner is constantly connected to an AC outlet, even whenit is not in use (e.g., at night and on holidays). However, when theapparatus is in the power OFF state or the AC adaptor is removed fromthe apparatus, the AC adaptor connected to the AC outlet continues to beconductive, so that a problem arises concerning power consumption duringthis period. While an AC adaptor includes a transformer for transforminga DC voltage, control, using an analog switch such as an FET switch, isperformed on the primary coil side of the transformer in order tostabilize the voltage output. Regardless of whether a PC is powered offor the AC adaptor is removed from the PC, so long as the AC adaptor isinserted into the outlet and is receiving AC power, the switchingcontrol is constantly performed. That is, power consumed by the ACadaptor is mainly that required by the switching control. In addition,since most of the power loss is converted into thermal energy, acountermeasure is also required that will disperse heat from the ACadaptor.

The following is a calculation of the power consumed by an AC adaptornot in use. As an example, a current resonant AC adaptor, which is usedfor a typical notebook PC, the “IBM ThinkPad” series, consumes 2 to 4 Wof power because of switching loss, even when the PC is in the power offstate, and a “flyback” AC adaptor consumes 0.5 to 1 W of power.Generally, since current resonant AC adaptors have superior voltageconversion efficiency, they tend to be used instead of the flyback ACadaptors, even though when not in use, the power loss for the currentresonant type is greater. Further, since even inside a PC a DC voltage(e.g., 16 V) is constantly applied by an AC adaptor, approximately 0.5 Wof power is consumed in the power off state. Although the power lossattributable to a single PC is relatively minute, being approximately 3W, at an office wherein a large number of PCS are installed, merely bykeeping AC adopters attached to AC power sources, a considerable chargefor electricity can be accrued.

Assuming that the period of time during which PCS are not used at nighton weekdays is 12 hours, and that the period of time during which PCSare not used on weekends is 60 hours. The total time in a year that a PCis not used is 1,280 hours/year (=12 hours/day×200 days/year+60hours/week×4 weeks/month×12 months/year). Therefore, if there were onemillion notebook PCS connected to AC adopters, the accompanying annualpower loss would be 15,840,000 KWh/year (=1,000K units×1,280hours/year×3 W), and assuming, e.g., the charge for electricity is239,184K yen (=0.0151K /KWh/year×15,840,000 KWh/year).

Since an AC power source is unlimited, from the standpoint of supplyingpower for driving PCS, practically no problems exist. However, whenconsideration is given to the sociobiological aspect, i.e., from theviewpoint of the effective use of resources and of environmentalprotection globally, such a power loss as that attributable to the ACadaptors that are not in use state can not be ignored.

In order to eliminate the loss of power at an AC adaptor not in usestate, it is preferable that the AC adaptor be detached from an outletand a notebook PC each time after it has been used. However, theconnection and the disconnection of cables are burdensome tasks, andthey contribute to the deterioration of usability. In addition, thefrequent disconnection of an AC adaptor accelerates the wear and tearexperienced by an outlet and the plug of an AC adaptor. And also, sincea notebook PC recharges its incorporate battery using power supplied inthe power-off state, a user must keep an AC adaptor attached.

Another method may be employed whereby in a state where the output fromthe AC adaptor is unnecessary (i.e., a period during which the main boxof a PC is powered off and is not being recharged) a signal to thiseffect is output by a notebook PC, and upon the receipt of this notice,the AC adaptor cuts off power to the primary coil side of thetransformer. In IBM Technical Disclosure Bulletin No. JA8-97-0299, forexample, there is disclosed an invention that embodies a method foradding a new signal line along which a notebook PC transmits the powersupply state signals to an AC adaptor to halt the operation of the ACadaptor. However, the addition of a signal line is accompanied by a lossof the connection compatibility at a DC inlet that connects the PC andthe AC adaptor. In other words, the notebook PC according to IBM TDBJA8-97-0299 accepts only the AC adaptor that is described in thatdisclosure. Also, this AC adaptor can be employed only for that notebookPC according to IBM TDB JA8-97-0299.

A technique for avoiding power loss due to an AC adaptor when anapparatus is not in use is disclosed in Japanese Unexamined PatentPublication Nos. Hei 6-292362, Hei 4-165957, Hei 7-153582 and Hei8-179858. However, since in Japanese Unexamined Patent Publication No.Hei 6-292363 a battery in the apparatus is used to turn on the primaryside switch of an AC adaptor, the operation of the AC adaptor can not behalted if there is no battery incorporated in the apparatus or if thereis no power remaining in an incorporated battery.

The invention disclosed in Japanese Unexamined Patent Publication No.Hei 4-165957 detects the presence of a load current in an AC adaptor tocontrol the on/off state of the AC adaptor. Therefore, when an apparatusthat has no incorporated battery is powered on, the AC adaptor can notdetect a change (or an event) in the state wherein the supply of powershould be initiated. That is, there occurs a contradiction that affectsthe AC adaptor and prevents it from being turned on again.

In Japanese Unexamined Patent Publication No. Hei 7-153582 there isdisclosed a power saving technique for an AC adaptor used forluminaries. In this publication, the AC adaptor is integrally formedwith a luminary, and the power saving technique for an AC adaptor thatis connected to the main box of an apparatus is not taught.

In Japanese Unexamined Patent Publication No. Hei 8-179858, a powerswitch is provided for an AC adaptor. When this power switch is manuallyoperated, the AC adaptor can be turned on and off, without removing theAC adaptor from an AC outlet. However, the AC adaptor can not be turnedoff automatically. For example, it is impossible for the AC adaptor tobe turned off automatically in response to completion of the rechargingprocess for the apparatus in the power-OFF state.

SUMMARY OF THE INVENTION

It is one object of the present invention to provide a superior ACadaptor for transforming an AC voltage into a DC voltage, and abattery-operated electronic apparatus that can employ such an ACadaptor. It is another object of the present invention to provide asuperior AC adaptor that can reduce power in the not in use state, and abattery-operated electronic apparatus that can employ such an ACadaptor. It is an additional object of the present invention to providea superior AC adaptor for which power consumption can be reduced in theunused state by detecting the condition of the power supply in anelectronic apparatus that is connected to the AC adaptor, and abattery-operated electronic apparatus that can employ such an ACadaptor.

To achieve the above objects, according to a first aspect of the presentinvention, an AC adaptor for transforming an AC voltage into a DCvoltage includes an input line along which an external AC voltage isinput, an AC/DC transformer for transforming the input AC voltage into aDC voltage, an output line along which the resultant DC voltage isoutput externally; and means for monitoring a voltage level across theoutput line and for halting an operation of the AC/DC transformer whenthe voltage level exceeds a predetermined value.

According to a second aspect of the present invention, an AC adaptor fortransforming an AC voltage into a DC voltage includes an input linealong which an external AC voltage is input; an AC/DC transformer fortransforming the input AC voltage into a DC voltage, an output linealong which the resultant DC voltage is output external, and means formonitoring a voltage level across the output line and for detaching theinput line from the AC/DC transformer when the voltage level exceeds apredetermined value.

According to a third aspect of the present invention, an AC adaptor fortransforming an AC voltage into a DC voltage includes (a) an input linealong which an external AC voltage is input, (b) a first transformer fortransforming the input AC voltage into a DC voltage at a first voltagelevel, (c) a switch provided on the primary side of the firsttransformer, (d) an output line along which a DC voltage on thesecondary side of the first transformer is output externally, (e) asecond transformer for transforming the input AC voltage into a DCvoltage at a second voltage level that is higher than the first voltagelevel, and for outputting the resultant DC voltage to the output line,and (f) an AC adaptor operation control circuit for comparing a voltagelevel across the output line with a reference voltage level, which ishigher than the first voltage level and which is lower than the secondvoltage level, and for turning on the switch when the voltage levelacross the output line is lower than the reference voltage level, or forturning off the switch when the voltage level across the output lineexceeds the reference voltage level.

According to a fourth aspect of the present invention, an electronicapparatus, which can be operated by at least either one of a DC voltagefrom an AC adaptor and a DC voltage from a battery, includes means fordetermining whether the electronic apparatus requires an external powersource, and means for detaching an input line of an AC adaptor from theelectronic apparatus when the electronic apparatus does not require anexternal power source.

According to a fifth aspect of the present invention, an electronicapparatus, which can be operated by at least either one of a DC voltagefrom an AC adaptor and a DC voltage from a battery, includes an inputline along which is fed a DC voltage from the AC adaptor, a power switchfor instructing that a power source be turned on and off, a system loadfor consuming the DC voltage from the AC adaptor and the DC voltage fromthe battery, a charging controller for controlling a charged state ofthe battery, and means for monitoring the ON/OFF state of the powersource and the recharged state of the battery and for detaching theinput line from the outside when the power source is turned off and whenthe battery is not to be recharged.

According to the present invention, the AC adaptor includes the firsttransformer, for transforming an AC voltage from an external AC powersource into a DC voltage to be supplied to an electronic apparatus, andthe second transformer for transforming the external AC voltage intoanother DC voltage. These DC voltages are supplied to the output line.The DC voltage output by the first transformer is set to the firstvoltage level, and the DC voltage output by the second transformer isset to the second voltage level. The second voltage level is higher thanthe first voltage level. The first transformer serves as the main powersource for the electronic apparatus, and the second transformer servesas an auxiliary power source having a small capacity.

The first transformer generates a power voltage required for theoperation of a secondary power supply system that serves as a load.Generally, a switching control is constantly performed on the primaryside in order to maintain a constant output voltage as is well known.Power is consumed for this switching control. According to the presentinvention, another switch is provided on the primary side of the firsttransformer in order to halt the inflow of a current from an external ACpower source.

When the secondary power supply system that serves as a load is notactivated, and charging is not performed, the second transformersupplies a power voltage to only one part of the circuit for the ON/OFFcontrol of the power source. Only a low voltage need be output by thesecond transformer, i.e., only a small power supply capability isrequired (e.g., about 10 mA). Therefore, the second transformer can be asimple transformer coupler and a current circuit. Further, unlike thefirst transformer, power produced by the second transformer is notconsumed by the switching operation. Since the amount of a current to behandled is extremely small compared with that for the first transformer,even when a switching type is employed for the second transformer, thepower consumed by the switching operation on the primary side of thesecond transformer will be extremely small.

The output voltage level of the AC adaptor is constantly compared withthe reference voltage. The reference voltage is set to a value that ishigher than the first voltage level and is lower than the second voltagelevel. When the electronic apparatus to which the AC adaptor isattached, is in the ON state (including when the battery is beingrecharged while the power is off), a electric charge is pulled in by thesystem load in the apparatus, so that the voltage across the output lineof the AC adaptor will go lower than the reference voltage. In responseto the result of a comparison, the switch on the primary side of thefirst transformer is turned on, and the AC adaptor is driven. That is,the DC voltage can be supplied by the first transformer.

When an electronic apparatus attached to an AC adaptor is powered offand the charging of a battery is not performed, the output line of theAC adaptor is detached from the system load in the apparatus (i.e., isin the open state) and the supply of a current from the secondtransformer is enabled, so that the voltage across the output line ofthe AC adaptor exceeds the reference voltage. In response to the resultof the comparison, the switch on the primary side of the firsttransformer is turned off, and thus the operation of the firsttransformer can be halted. Therefore, since the consumption of powerthat accompanies the switching operation at the first transformer iseliminated, the power consumed can be reduced, even when the AC adaptoris connected to the outlet of the AC power source and to the apparatus.

The AC adaptor determines the power supplied state of the apparatus(i.e., determines whether the power is on or the battery is beingcharged) in accordance with the voltage level at the output line of theAC adaptor. In other words, since the number of signal lines need not beincreased for a power saving operation, the connector compatibility ofthe AC adaptor can be maintained.

The electronic apparatus of the present invention detaches the inputline of the AC adaptor when it does not require an external supply ofpower. As for the AC adaptor, since the output side is opened (or, isset to a high-impedance state), the voltage level at the output lineexceeds the reference voltage level and the operation of the firsttransformer can be halted. That is, the power reduction operation in theAC adaptor is ensured.

In short, when the AC adaptor according to the present invention isemployed for an electronic apparatus, power consumption by the ACadaptor while the power to the apparatus is off can be restrictedwithout detaching the AC adaptor from the DC inlet and the AC outlet.

Advantages of the Invention, as is described herein, according to thepresent invention include a superior AC adaptor for transforming an ACvoltage into a DC voltage, and a battery-operated electronic apparatusthat can employ such an AC adaptor. Further, according to the presentinvention, provided are a superior AC adaptor that can reduce power notin use state, and a battery-operated electronic apparatus that canemploy such an AC adaptor. In addition, according to the presentinvention, provided are a superior AC adaptor that detects the powersupply condition of an electronic apparatus attached to the AC adaptor,and a battery-operated electronic apparatus that can employ such an ACadaptor.

Other objects, features and advantages of the present invention willbecome apparent during the course of the following detailed descriptionof the preferred embodiment, given while referring to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a power supplying system foran AC adaptor and an electronic apparatus appropriate for the presentinvention.

FIG. 2 is a diagram illustrating the hardware block diagram of anelectronic apparatus 50 to which an AC adaptor 10 according to thepresent invention can be attached, and in particular, showing a powersupplying system.

FIG. 3 is a timing chart showing operating characteristics accompaniedby control procedures performed by a controller 90.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiment of the present invention will now be describedin detail while referring to the drawings.

A. Hardware Block Diagram

In FIG. 1 is shown an AC adaptor 10 appropriate for the presentinvention. The AC adaptor 10 in this embodiment transforms an AC voltageof 100 V received from an AC outlet into a DC voltage of 16 V, andsupplies the DC voltage to an electronic apparatus 50 via a DC outlet13. In order to implement AC-DC converter function, the AC adaptor 10includes a rectification bridge 11, for rectifying and smoothing an ACvoltage, and a transformer 12 for transforming an AC voltage into a DCvoltage at a predetermined level (16 V in this embodiment). The outputof the transformer 12 is the main power for the electronic apparatus 50.

The primary side of the transformer 12 is connected to the rectificationbridge 11, and the secondary side is connected to the electronicapparatus 50 via the DC outlet 13. An analog switch 14 is inserted intothe line leading to the primary side of the transformer 12, and when theanalog switch 14 is turned on or off, the supply of a current to thetransformer 12 is controlled. The feedback control of the analog switch14 is performed by a controller, not shown but of the usual nature, andas a result of the feedback control, a predetermined outputcharacteristic, such as a constant voltage (CV) output or a constantcurrent (CC) output, is provided for the DC output on the secondaryside. While the AC adaptor 10 is being driven, the analog switch 14 onthe primary side is repetitively turned on and off to control theoutput, and the consumption of extra power occurs due to the switchingloss that was hereinbefore described in the Background Art. The analogswitch 14 is, for example, an FET switch. The ACiDC transformationmechanism of the AC adaptor 10 may be either a current resonant type ora flyback type.

In addition to the AC/DC transformation mechanism, the AC adaptor inthis embodiment includes a switch 20 for halting the supply of a currentto the primary side of the transformer 12, and a control block 30 forturning on or off the switch 20. It should be fully understood that,since a current does not flow to the primary side coil of thetransformer 12 while the switch 20 is off, the switching loss incurreddue to the FET switch 14 is eliminated and the loss of power can berestricted.

The control block 30 comprises a control transformer 31, a comparator 32and a primary-secondary isolator 33. AC 100 V supplied via the AC outletis branched and input to the primary side of the control transformer 31.The control transformer 31 has a low output and serves as an auxiliarypower source. On the secondary side of the control transformer 31, apaired diode 35 and capacitor 36 rectifies and smooths the output, and asignal of DC 20 V is generated. The voltage level of 20 V is notrequired for the implementation of the present invention; however, thevoltage level should be sufficiently higher than 16 V, the output levelof the adaptor 10.

The output terminal of the control transformer 31 is connected via aresistor 37 to the 16 V output terminal of the AC adaptor 10 and also toone of the terminals of the comparator 32. When, in the power-OFF stateof the electronic apparatus 50 or during the charging of a battery 55,the current output by the control transformer 31 that flows from theoutput terminal of the AC adaptor 10 exceeds the permissible level, theresistor 37 reduces a voltage at the output terminal of the AC adaptor10. The resistance of the resistor 37 is set, for example, to 1 kΩ.Because of the existence of the resistor 37, the output of the controltransformer 31 is used only for the control of the switch 20, which willbe described later, and the loss of power can be avoided.

The comparator 33 compares a voltage output by the AC adaptor 10 withthe reference voltage. The reference voltage level is set higher than 16V, which is the output voltage during the normal operation of the ACadaptor, and lower than 20 V, which is a voltage output by the controltransformer 31. In this embodiment, 18 V is set as the referencevoltage.

When the output terminal of the AC adaptor 10 continues to be connectedto the system load in the electronic apparatus 50, an electric charge ispulled in by the system load, and as a result, a voltage of 16 V, whichis the output by the transformer 12, appears at the output terminal ofthe system load. When the output terminal of the AC adaptor 10 isdetached from the system load, i.e., is opened, a voltage of 20 V, whichis the output by the control transformer 31, appears at the outputterminal. Therefore, the comparator 32 determines whether the voltage atone input terminal is higher than the reference voltage of 18 V, whichis the voltage at the other input terminal, to ascertain whether thevoltage output by the AC adaptor 10 is being used for driving theelectronic apparatus 50 or whether the output terminal of the AC adaptoris connected to the electronic apparatus 50.

The output of the comparator 32 is used for controlling the ON/OFF stateof the switch 20. To electrically isolate a signal to the secondary sidefrom a signal to the primary side, the output of the comparator 32controls the switch 20 via the primary-secondary isolator 33. Theprimary-secondary isolator 33 may be, for example, a photo coupler,which is well known in the art.

When the voltage at one input terminal is lower than 18 V, i.e., whenthe output of the AC adaptor 10 is currently being consumed by theelectronic apparatus 50, the comparator 32 outputs a signal to turn onthe switch 20. Since, as a result, the current input via the AC outletis supplied to the transformer 12, the AC adaptor 10 can generate avoltage. When the voltage at one input terminal is higher than 18 V,i.e., when the output of the AC adaptor 10 is not being consumed by theelectronic apparatus 50, the comparator 32 outputs a signal to turn offthe switch 20. Since, as a result, the current input via the AC outletis not supplied to the transformer 12, the AC adaptor 10 falls into theoperation halted state. Accordingly, the switching loss due to the FETswitch 14 is restricted. It should be noted that the switch 20 is, forexample, an FET switch.

In FIG. 2 is shown the hardware block diagram of the electronicapparatus 50 to which the AC adaptor 10 of the present invention can beattached. In particular, the power supplying system is shown. Theelectronic apparatus 50 is a battery-operated, and is, for example, anotebook computer. The individual sections will now be described whilereferring to FIG. 2.

The electronic apparatus 50 receives a 16 VDC voltage from the ACadaptor 10 via a DC inlet 51 that is formed in the wall of the apparatus50. A power line 40 is connected to a DC/DC converter 53 via a pair ofFET switches FET1 and FET2. The FET switches FET1 and FET2 are soconnected that cathode terminals of parasitic diodes face each other.When both FET switches are turned off, the bidirectional supply of acurrent across the power line 40 can be halted. In this embodiment, theswitches FET1 and FET2 are a Nch type.

The DC/DC converter 53 receives, in parallel, an output terminal voltagefrom the battery 55, which is incorporated in the apparatus 50. Thebattery 55 generally is a battery pack that consists of a plurality ofrechargeable battery cells, such as Li-ion or NiMH cells. The inputterminal of a charger 54 is connected to the power line 40, and theoutput terminal is connected to the terminal of the battery 55. Thecharger 54 is a circuit for employing extra power produced by the ACadaptor 10 when the power to the apparatus 50 is off in order togenerate a charge current for the battery 55. The initiation and haltingof the charging is controlled by a power controller 70, which will bedescribed later.

The DC/DC converter 53 converts a DC voltage of 16 V supplied by the ACadaptor 10 to a voltage level (DC 5 V in this embodiment) appropriatefor driving the system, and stably outputs the voltage. The outputvoltage is supplied to the individual sections of a system load 60. Thesystem load 60 comprises various peripheral controller chips, includinga CPU 61, a main memory 62 and a video controller 63; a display 64 as anoutput device; and a hard disk drive (HDD) 65, a floppy disk drive (FDD)66 and a CD-ROM drive 67, all of which are external storage devices. TheDC/DC converter 53 is driven by an input voltage V_(CC) received fromthe AC adaptor 10.

The CPU 61 is a main controller for controlling the operation of theelectronic apparatus 50 under the control of an operating system (OS),and employs the main memory 62 as a work area. Necessary program codeand data are loaded as needed from an external storage device, such asthe hard disk drive (HDD) 65, into the main memory 62. The controllingof the operation of the peripheral devices is controlled by eachperipheral controller. For example, the drawing process on the display64 is controlled by the video controller 63, and the input/output ofdata for a modem and a printer are controlled by an I/O controller (notshown). The display 64 of the notebook PC is, generally, a liquidcrystal display (LCD), which is a thin and light, and consumes only asmall amount of power.

The electronic apparatus 50 has in addition a power controller 70 and apower-ON logic circuit 80 to implement the operation for supplying powerto the apparatus 50 and for halting the supply of power. The powercontroller 70 is a dedicated controller for controlling the powersupplying system in the electronic apparatus 50. The power controller 70includes, for example, (1) a function for monitoring the operation ofthe apparatus 50 and power consumption, and (2) a function forconstantly monitoring the remaining power capacity of the battery 55 andfor initiating and halting the charging operation performed by thecharger 54. The power controller 70 includes input terminals (not shown)for measuring the terminal voltage of the battery 55, the amount of acurrent that flows in and out and the ambient temperature of the batterycell, and can ascertain the charged state of the battery 55. Inaddition, during the charging period, the power controller 70 asserts acharge-ON (CHGON) signal to drive the charger 54. When the charging isterminated, the power controller 70 negates the charge-ON (CHGON)signal. A one-chip microprocessor “H8,” produced by Hitachi Ltd., canprogram such an operation as that performed by the power controller 70.

In response to a user's manipulation of a power switch 59, which isformed on the wall of the electronic apparatus 50, the power-ON logiccircuit 80 performs the power ON/OFF operation for the electronicapparatus 50. When the power to the apparatus 50 is on, the power-ONlogic circuit 80 asserts a power-ON (PWRON) signal, and when the powerto the apparatus 50 is off, the power-ON logic circuit 80 negates thepower-ON (PWRON) signal. The power controller 70 is driven at the outputvoltage V_(CC5) roduced by the DC/DC converter 53, while the power-ONlogic circuit 80 is driven at the input voltage V_(CC) received from theAC adaptor 10.

In this embodiment, when the supply of power from the AC adaptor 10 isnot required, the electronic apparatus 50 detaches the power line 40from the DC inlet 51, so that the consumption of extra power by thesystem load 60 can be prevented, even when the AC adaptor 10 is attachedto the apparatus 50. When the supply of power from the AC adaptor 10 isnot required is the time at which the power to the apparatus 50 is offand the charging of the battery 55 is terminated. The disconnection ofthe power line 40 from the DC inlet 51 is accomplished by turning offthe switches FET1 and FET2, as is described above. A controller 90enclosed by the broken line in FIG. 2 is mounted in order to implementthe ON/OFF control of the switches FET1 and FET2. The individualelements in the controller 90 are driven at an input voltage V_(CC)received from the AC adaptor 10. FIG. 3 is a timing chart showing theoperating characteristics of the controller 90. The functions of thecontroller 90 will now be described while referring to FIG. 3.

(a) Insertion of AC Adaptor

Assume that the AC adaptor 10 is attached to the DC inlet 51 of theapparatus 50 while the power to the apparatus 50 is off. A voltageoutput by the AC adaptor 10 is applied to the power line 40. The voltageoutput by the AC adaptor 10 is a DC voltage of 16 V generated by thetransformer 12. In response to the start of the supply of power by theAC adaptor 10, a pulse wave generated by the interaction of a resistorR1 and a capacitor C1 is input to a reset terminal R of a flip-flop F/Fin the controller 90, while a pulse wave generated by the interaction ofa resistor R2 and a capacitor C2 is input to a set terminal S of theflip/flop F/F. In this embodiment, parameters for resistances andcapacities are so set that the leading edge of the pulse wave at thereset terminal R is delayed. Therefore, the resetting of the flip-flopF/F is performed first, and the output Q of the flip-flop F/F ismaintained at low. The low output Q is transmitted to the gate of an NchFET switch FET3, which is then turned off, and the gates of the switchesFET1 and FET2 are detached from the ground and go high, so that theswitches FET1 and FET2 are set to the ON state. In other words, thepower line 40 is connected. In response to the ON states of the FETswitches, the DC/DC converter 53 is driven and begins to output a 5V DCvoltage V_(CC5).

(b) Initiation of Charging

The power controller 70 measures the time for starting the chargingprocess. The power controller 70 constantly monitors the remaining powerand the terminal voltage of the battery 55, or the ambient temperatureof the battery cell, and detects a charging start time when theremaining power or the terminal voltage, or the ambient temperaturefalls below a predetermined value which is a well known factor. When thecharging start time is detected while the AC adaptor 10 is attached, thepower controller 70 asserts its output signal CHGON. The signal CHGON istransmitted to the charger 54 to drive it. In addition, the CHGON signalis inverted by a transistor TR2, and the inverted signal is transmittedas a low-level CHGOFF signal to one of the terminals of a NAND gate. Atthis time, the electronic apparatus 50 is in the OFF state, and thepower-ON logic circuit 80 continues the negation of its output signalPWRON. The PWRON signal is inverted by a transistor TR1, and theinverted high-level PWROFF signal is transmitted to the other terminalof the NAND gate. Therefore, at the same time the charging is begunwhile the power to the apparatus 50 is off, the output of the NAND gateis changed from low to high. Since the output of the NAND gate does notaffect the input of S to the flip-flop F/F, the ON states of theswitches FET1 and FET2 are maintained. In other words, the supply ofcharging power from the AC adaptor 10 is ensured.

(c) Termination of Charging

The power controller 70 measures the time for the completion of thecharging process. The power controller 70 constantly monitors the poweraccumulated and the terminal voltage of the battery 55, or the ambienttemperature of the battery cell, and detects a charging end time whenthe power accumulated or the terminal voltage, or the ambienttemperature exceeds a predetermined value, a well known factor. When thecharging end time is detected while the AC adaptor 10 is attached, thepower controller 70 negates its output signal CHGON. The signal CHGON istransmitted to the charger 54 to halt the charging operation. Further,the CHGON signal is inverted by the transistor TR2, and the invertedhigh-level CHGOFF signal is transmitted to one of the terminals of theNAND gate. At this time, the electronic apparatus 50 is in the OFFstate, and the power-ON logic circuit 80 continues negation of itsoutput signal PWRON. The PWRON signal is inverted by the transistor TR1,and the inverted high-level PWROFF signal is transmitted to the otherterminal of the NAND gate. Therefore, at the same time the charging isterminated while the power to the apparatus 50 is off, the output of theNAND gate is changed from high to low. Due to the trailing edge of theNAND output, a pulse wave is generated by the interaction of theresistor R2 and the capacitor C2 and is transmitted to the set terminalS of the flip-flip F/F. As a result, the internal state of the flip-flopF/F is shifted and its output Q is changed to high. Thus, a high voltageis applied to the gate of the switch FET3, which is then turned on. Thegates of the switches FET1 and FET2 fall to the ground level, and theswitches FET1 and FET2 are turned off. In other words, the power line 40is detached from the DC inlet 51.

(d) Power ON

The power-ON operation is initiated by, for example, the manipulation ofa power-ON switch 81 formed on the wall of the case of the electronicapparatus 50. In response to the manipulation of the power-ON switch 81,the power-ON logic circuit 80 begins a predetermined power-ON operationsequence, and asserts its output signal PWRON. The PWRON signal istransmitted via a capacitor C3 to the base of a transistor TR3, and apulse wave is generated at the collector of the transistor TR3. Thepulse wave is transmitted to the reset terminal R of the flip-flop F/F,which changes its output Q to low. Since the low output Q is transmittedto the gate of the Nch switch FET3, the FET3 detaches the gates of theswitches FET1 and FET2 from the ground and drives them to high, so thatthe switches FET1 and FET2 are turned on. In short, the connection ofthe power line 40 is established. In response to the ON states of theFET switches, the DC/DC converter 53 is driven to begin to output a 5VDC voltage V_(CC5).

(e) Initiation of Charging in Power ON State

The power controller 70 measures the time for starting the chargingprocess. The power controller 70 constantly monitors the power remainingand the terminal voltage of the battery 55, or the ambient temperatureof the battery cell, and detects the charge start time when theremaining power or the terminal voltage, or the ambient temperaturefalls below a predetermined value (well known). When the charging starttime is detected while the power to the apparatus 50 is on, the powercontroller 70 asserts its output signal CHGON. The signal CHGON istransmitted to the charger 54 to drive it. In addition, the CHGON signalis inverted by the transistor TR2, and the inverted signal istransmitted as a low CHGOFF signal to one of the terminals of the NANDgate. At this time, the electronic apparatus 50 is in the ON state, andthe powerON logic circuit 80 continues the assertion of its outputsignal PWRON. The PWRON signal is inverted by the transistor TR1, andthe inverted low PWROFF signal is transmitted to the other terminal ofthe NAND gate. Therefore, even when the charging is begun while thepower to the apparatus 50 is on, the output of the NAND gate ismaintained at high and thus does not affect the input of S to theflip-flop F/F, and the ON states of the switches FET1 and FET2 can bemaintained. In other words, the connection of the power line 40 ismaintained, and the supply of charging power from the AC adaptor 10 isensured.

(f) Termination of Charging in Power ON State

The power controller 70 measures the time for completion of the chargingprocess. The power controller 70 constantly monitors the poweraccumulated and the terminal voltage of the battery 55, or the ambienttemperature of the battery cell, and detects a charging start time whenthe power accumulated or the terminal voltage, or the ambienttemperature exceeds a predetermined value, as before stated to be wellknown. When the charging end time is detected while the power to theapparatus 50 is on, the power controller 70 negates its output signalCHGON. The signal CHGON is transmitted to the charger 54 to halt thecharge operation. In addition, the CHGON signal is inverted by thetransistor TR2, and the inverted high CHGOFF signal is transmitted toone of the terminals of the NAND gate. At this time, the electronicapparatus 50 is in the ON state, and the power-ON logic circuit 80continues assertion of its output signal PWRON. The PWRON signal isinverted by the transistor TR1, and the inverted low PWROFF signal istransmitted to the other terminal of the NAND gate. Therefore, at thesame time the charging is terminated while the power to the apparatus 50is on, the output of the NAND gate is maintained high and does notaffect the input of S to the flip-flop F/F, and the ON states of theswitches FET1 and FET2 are maintained. In other words, the connection ofthe power line 40 is maintained, and the supply of charging power fromthe AC adaptor 10 is ensured.

(g) Power OFF

The power-OFF operation is initiated by, for example, manipulating apower-ON switch 81 formed on the wall of the case of the electronicapparatus 50. In response to the manipulation of the power-ON switch 81,the power-ON logic circuit 80 begins a predetermined power-OFF operationsequence, and negates its output signal PWRON. The PWRON signal isinverted by the transistor TR1, and the inverted high PWROFF signal istransmitted to one of the terminals of the NAND gage. Since the chargingof the battery 55 is terminated at this time, the power controller 70negates its output signal CHGON, and a high CHGOFF signal is transmittedto the other terminal of the NAND gate. In response to the power-OFFoperation, the NAND gate changes its output from high to low. Due to thetrailing edge of the NAND output, a pulse wave is generated by theinteraction of the resistor R2 and the capacitor C2, and is transmittedto the set terminal S of the flip-flip F/F. As a result, the internalstate of the flip-flop F/F is shifted and its output Q is changed tohigh. Thus, a high voltage is applied to the gate of the switch FET3,which is then turned on. The gates of the switches FET1 and FET2 fall tothe ground level, and the switches FET1 and FET2 are turned off. Inother words, the power line 40 is detached from the DC inlet 51.

(h) Battery Exchange

The period during which the power to the apparatus 50 is off is adesirable time for a user to exchange the battery 55. At the moment anew battery 55 is loaded, a battery terminal voltage (PVBATT) is appliedto an output terminal 55 a, and accordingly, a voltage is applied viathe capacitor C3 to the base of the transistor TR3 to generate a pulsewave at the collector of the transistor TR3. The pulse wave istransmitted to the reset terminal R of the flip-flop F/F, which changesits output Q to low. When the low output Q is transmitted to the gate ofthe Nch FET switch FET3, since the FET3 detaches the gates of theswitches FET1 and FET2 from the ground to high, the FET3 turns on theswitches FET1 and FET2. In short, the connection of the power line 40 isestablished. In response to the ON status of the FET switches, the DC/DCconverter 53 is activated to begin to output the 5V DC voltage V_(CC5).Upon the exchange of a battery, generally, a charging process should beperformed for a new battery 55. In this embodiment, the connection ofthe power line 40 is ensured at the battery exchange, so that thecharging process can be performed.

(I) Initiation of Charging

The power controller 70 measures the time for starting the chargingprocess. The power controller 70 constantly monitors the power remainingand the terminal voltage of the battery 55, or the ambient temperatureof the battery cell, and detects a charging start time when the powerremaining or the terminal voltage, or the ambient temperature fallsbelow a predetermined value. When the charging start time is detectedwhile the power to the apparatus 50 is off, the power controller 70asserts its output signal CHGON. The signal CHGON is transmitted to thecharger 54 to drive it. In addition, the CHGON signal is inverted by thetransistor TR2, and the inverted low CHGOFF signal is transmitted to oneof the terminals of the NAND gate. At this time, the electronicapparatus 50 is in the OFF state, and the power-ON logic circuit 80continues the negation of its output signal PWRON. The PWRON signal isinverted by the transistor TR1, and the inverted high PWROFF signal istransmitted to the other terminal of the NAND gate. Therefore, at thesame time the charging is begun while the power to the apparatus 50 isoff, the output of the NAND gate is changed from low to high. Since theoutput of the NAND gate does not affect the input of S to the flip-flopF/F, the ON states of the switches FET1 and FET2 are maintained. Inother words, the supply of charging power from the AC adaptor 10 isensured.

In the above description, in a period during which the electronicapparatus 50 does not require the supply of power, more specifically, ina period such as the phase (c) or (g) during which the power to theapparatus 50 is off and the charging has been terminated, the power line40 is detached by the switches FET1 and FET2. The ON/OFF control of theswitches FET1 and FET2 is performed based on the voltage received fromthe AC adaptor 10 applied to the DC inlet 51. In other words, theelectric charges accumulated in the battery 55 of the apparatus 50 arenot consumed by the switching control.

Although many electric circuits other than those shown in FIG. 1 arerequired to construct the AC adaptor 10 and the electronic apparatus 50,which is a computer system, they are well known to one having ordinaryskill in the art. And as they are not directly related to the subject ofthe present invention, no explanation for them will be given. Further,it should be noted that, to avoid making the drawings too complex, onlyone part of the connections between the hardware blocks in the drawingsis shown.

B. Operating Characteristics of AC Adaptor

Power saving characteristics of the AC adaptor 10 according to thisembodiment will now be described. As was previously described, aconventional AC adaptor continues to consume power as long as it isattached to an AC outlet. It will be apparent from the followingexplanation, however, that the AC adaptor 10 in this embodiment does notsubstantially consume power unless the electronic apparatus 50 attachedthereto requires power. An explanation will now be given while referringto FIG. 1 again.

(a) When an AC adaptor 10 is connected to an AC outlet but is notconnected to an electronic apparatus:

since a current flows in the transformer 12 when the AC adaptor 10 isconnected to the AC outlet, power may be consumed by the ON/OFF controlof the FET switch 14.

When the AC adaptor 10 is not connected to the electronic apparatus 50however, the output terminal (the DC outlet 13) of the AC adaptor 10 isin the open state.

Whereas, not only a voltage output by the power supply transformer 12but also a voltage output by the control transformer 31 is applied tothe output terminal of the AC adaptor 10, in the open state of theoutput terminal, a higher voltage of 20 V is output by the transformer31. As a result, the output of the comparator 32 is asserted, and theswitch 20 is turned off via the primary-secondary isolator 33. As aresult, no current flows in the transformer 12, and the consumption ofpower by the ON/OFF control of the FET switch 14 can be avoided.

(b) When an AC adaptor 10 is connected to both an AC outlet and anelectronic apparatus:

when the AC adaptor 10 is continuously connected to the electronicapparatus 50, power may be consumed by the system load of the apparatus50 even if the power to the apparatus 50 is off.

In this embodiment, however, when the power to the electronic apparatus50 is off and the charging has been terminated, the power line 40 isdisconnected by the FET switches FET1 and FET2 as previously described.Specifically, in a period during which the apparatus 50 does not requirepower, the output terminal (the DC outlet 13) of the AC adaptor 10 is inthe open state.

Whereas, not only a voltage output by the power supply transformer 12but also a voltage output by the control transformer 31 is applied tothe output terminal of the AC adaptor 10, in the open state of theoutput terminal, a higher voltage of 20 V is output by the transformer31. As a result, the output of the comparator 32 is asserted, and theswitch 20 is turned off via the primary-secondary isolator 33. As aresult, no current flows in the transformer 12, and the consumption ofpower by the ON/OFF control of the FET switch 14 can be avoided.

The present invention has been described in detail while referring to aspecific embodiment. However, it should be obvious to one havingordinary skill in the art that various modifications or revisions of theembodiment are possible within the scope of the present invention. Thepresent invention can be applied, for example, for facsimile machines,various cordless devices, such as mobile radio terminals, cordlesstelephones, personal digital assistants and video cameras, variousbattery-operated electric/electronic devices, such as word processors,and electric/electronic devices to be driven by AC power via an ACadaptor. That is, although the present invention has been disclosed byusing an example, it should not be limited to that example. To fullyunderstand the subject of the present invention, the claims should bereferred to.

What is claimed:
 1. An AC adaptor independent of and for connecting toan electronic apparatus having a load operable by a DC voltage,comprising: a first connector for directly connecting to an external ACvoltage source, said first connector receiving alternating current fromsaid external AC voltage source; means for generating a DC voltage; asecond connection for connecting to the electronic apparatus by an inputline for supplying the DC voltage for operation of the load of theelectronic apparatus; means included as a part of the AC adaptor fordetermining whether the load of the electronic apparatus requires a DCvoltage for operation of the load of the electronic apparatus; and meansincluded as a part of the AC adaptor for automatically disconnecting themeans for generating the DC voltage of the AC adaptor from the externalAC voltage source when the load of the electronic apparatus does notrequire power from the AC adaptor power source to operate.
 2. The ACadaptor as defined in claim 1, wherein the means for automaticallydisconnecting the means for generating the DC voltage of the AC adaptorfrom the external AC voltage source when the load of the electronicapparatus does not require power from the AC adaptor power source tooperate, also provides for automatically disconnecting the means forgenerating the DC voltage of the AC adaptor from the external AC voltagesource when the load of the electronic apparatus does not require powerfrom a battery utilized as an alternate power source of DC voltage tothe load of the electronic apparatus.
 3. The AC adaptor as defined inclaim 2, wherein the means for automatically disconnecting the means forgenerating the DC voltage of the AC adaptor from the external AC voltagesource when the load of the electronic apparatus does not require powerincludes comparator means for determining that the electronic apparatusdoes not require power.
 4. The AC adaptor as defined in claim 3, furtherincluding a charging controller for controlling a charged state of thealternate DC power source battery; and wherein the means forautomatically disconnecting the means for generating the DC voltage ofthe AC adaptor from the external AC voltage source when the load of theelectronic apparatus does not require power, includes means formonitoring the connective state of the power source AC adaptor to theexternal AC voltage source and the recharged state of the alternate DCpower source battery and for automatically disconnecting the AC adaptorpower source from the AC power source when the electronic apparatus doesnot require power and when the alternate DC power source battery is notto be recharged.
 5. The AC adaptor as defined in claim 4, wherein themeans for monitoring the connective state of the power source AC adaptorto the external AC voltage source and the recharged state of the batteryand for automatically disconnecting the AC adaptor power source from theAC power source when the electronic apparatus does not require power andwhen the alternate DC power source battery is not to be recharged,includes a connection to the AC voltage source which is used to generatethe DC voltage for operation of the load of the electronic apparatus.